G. FLUSTRA. 51 



On the fossils of the chalk in the vicinity of 

 Paris. 



SMALL-MOUTHED. (FOSSIL.) 



30. Flustra microstoma. Rather thick incrustation, 

 with cells not very distinct, oval, and rather prominent 

 the opening in the middle, very round and small. 



On the large fossil oyster in the vicinity of Sceaux. 



DEPRESSED. 



37. Flustra depressa. Cells oval, alternate, hori- 

 zontal, and slightly punctured ; openings half-moon 

 shaped, and closed with a valve. 



Adriatic. 



dish-shaped. 



38. Flustra patellaria. Cells oval, flat above and 

 convex below ; nearly isolated, horizontal, and sub- 

 alternate. 



Mediterranean. 



oblate. 



39. Flustra planata. Cells oval, flat, alternate, 

 and distant, bordered and closed by a membrane. 



Mediterranean. 



The succeeding genera belonging to this Order 

 have hitherto been included in the general denomina- 

 tion of Cellarias: but their varieties induced me to 

 separate them into families ; whose species are indeed 

 few, but which will probably be augmented when these 

 little beings shall have been more attentively studied. 



These Polypidoms are plant-like, frequently arti- 

 culated, either flat, compressed, or cylindrical. Ceils 



